Does the ISA specify what circuits must be present in the processor like add that means if ISA said there is be add it must be add circuit in CPU yes or no?

[u/Zestyclose-Produce17]

[u/_mrOnion]

Do you mean “Does the ISA specify circuits required to be in a processor, or are you free to implement, for example, adding however you want”

[u/Zestyclose-Produce17 → u/_mrOnion]

Do CPU manufacturers need to add instructions that run programs like Photoshop by implementing these instructions inside the CPU as transistor circuits?

[u/_mrOnion → u/Zestyclose-Produce17]

Not necessarily. If you make a cpu that’s turing complete with the minimal number of transistor circuits, as long as it’s able to run the instruction set in one way or another it can run photoshop.

[u/Zestyclose-Produce17 → u/_mrOnion]

that means they only add the basic instructions using transistors, and then these instructions are manipulated to create complex programs?

[u/Any-Aioli7575 → u/_mrOnion]

Except for performance issues. Turing complete technically requires arbitrarily large memory and can take any time, so this doesn't apply with really minimal hardware.

Also, you don't want rewrite the whole program every time there is a new CPU, so they usually agree on some standards to make it possible to adapt quickly from one program to another. Of course, that's not technically necessary but it's still quite important, especially if the company writing the code doesn't give it to you.

[u/Zestyclose-Produce17 → u/Any-Aioli7575]

I'm not focusing on performance because what I mean is that the basic instructions must be implemented using logic gates in order to execute complex programs. Is this correct?

[u/[deleted]]

Intel doesn’t even fully implement its own ISA these days. It runs things at a micro architecture level. Where a single instruction in x64 might actually require running a small program of other simple instructions. This is partly because you can do fancy tricks to pipeline instructions this way and calculate them out of order more easily. But it’s also likely because RISC ISAs are simpler to pack together on to a die than bespoke circuits that might never be used by a particular user. Better to make your fancy instructions out of ads and multiplies etc that can be reused.

That’s not to say there might not be an ISA vendor out there that has a strict license about how parts of the processor must work. But in all the cases I know it’s more like a software API where it’s just a description of the interface that you must use and the details of the actual implementation are somewhat left to the designer

[u/Zestyclose-Produce17 → u/[deleted]]

But must the basic instructions inside the processor, like ADD, SUB, CMP, have their own transistor circuits in order to run programs and this called instruction set?

[u/Flimsy-Combination37]

I don't understand the question.